网络边界桥接指攻击者通过控制网络边界设备（如防火墙、路由器）突破网络隔离策略，构建跨安全域通信通道的技术手段。传统防御依赖流量策略审查、设备配置监控及异常规则检测，通过比对设备配置快照与网络流量日志识别未授权策略变更。
为规避传统检测机制，攻击者发展出非策略修改型桥接技术，通过功能滥用、协议嵌套和管理接口劫持等手法，在不触发策略告警的前提下实现边界穿透，形成"策略合规、行为异常"的新型攻击范式。
现有匿迹桥接技术的共性在于深度利用网络设备的固有功能特性和协议解析漏洞：流量镜像隐蔽转发技术挖掘镜像端口的监控盲区，将跨域通信伪装成运维数据采集；协议隧道嵌套桥接技术通过协议栈的纵向深度扩展，在单层合规的前提下实现多层穿透；合法管理接口滥用则借助设备信任链的脆弱性，将攻击流量融入日常运维流。三类技术的核心突破在于解耦策略变更与边界穿透的必然关联，通过协议语义的创造性重构和设备功能的非常规利用，使恶意行为获得表面合法性。技术演进呈现三个趋势：从规则篡改转向功能滥用、从单层协议突破转向多维协议嵌套、从主动连接建立转向被动流量劫持。
匿迹技术的成熟使得传统基于策略审计的防御体系面临严峻挑战，防御方需构建协议栈深度行为分析、管理接口异常操作检测等能力，并引入设备固件完整性验证机制，实现对隐蔽桥接行为的多维度感知与阻断。
| 效应类型 | 是否存在 |
|---|---|
| 特征伪装 | ✅ |
| 行为透明 | ✅ |
| 数据遮蔽 | ✅ |
| 时空释痕 | ❌ |
攻击者通过协议嵌套和功能模拟实现流量特征伪装。例如将恶意隧道封装在标准管理协议（SNMP/NETCONF）中，严格遵循协议交互规范，使桥接流量在报文结构、交互时序等方面与合法管理操作高度一致，规避基于协议特征识别的检测系统。
技术实现过程中利用设备固件漏洞或零日攻击获取控制权，在未触发安全告警的前提下完成边界穿透。例如通过内存攻击获取镜像端口配置权限，或利用未公开的管理接口漏洞建立隐蔽信道，使得防御方难以感知设备已被植入桥接功能。
跨域通信普遍采用多层加密（如TLS隧道嵌套IPsec），在协议封装阶段对载荷内容进行加密混淆。管理接口滥用场景中，攻击者还会利用协议自身的加密特性（如NETCONF over SSH）隐藏传输内容，使得流量解密前无法识别攻击意图。
| ID | Name | Description |
|---|---|---|
| G0096 | APT41 |
APT41 used |
| ID | Mitigation | Description |
|---|---|---|
| M1043 | Credential Access Protection |
Some embedded network devices are capable of storing passwords for local accounts in either plain-text or encrypted formats. Ensure that, where available, local passwords are always encrypted, per vendor recommendations.[2] |
| M1037 | Filter Network Traffic |
Upon identifying a compromised network device being used to bridge a network boundary, block the malicious packets using an unaffected network device in path, such as a firewall or a router that has not been compromised. Continue to monitor for additional activity and to ensure that the blocks are indeed effective. |
| M1032 | Multi-factor Authentication |
Use multi-factor authentication for user and privileged accounts. Most embedded network devices support TACACS+ and/or RADIUS. Follow vendor prescribed best practices for hardening access control.[3] |
| M1027 | Password Policies |
Refer to NIST guidelines when creating password policies. [4] |
| M1026 | Privileged Account Management |
Restrict administrator accounts to as few individuals as possible, following least privilege principles. Prevent credential overlap across systems of administrator and privileged accounts, particularly between network and non-network platforms, such as servers or endpoints. |
| ID | Data Source | Data Component | Detects |
|---|---|---|---|
| DS0029 | Network Traffic | Network Traffic Content |
Monitor and analyze traffic patterns and packet inspection associated to protocol(s) that do not follow the expected protocol standards and traffic flows (e.g extraneous packets that do not belong to established flows, gratuitous or anomalous traffic patterns, anomalous syntax, or structure). Consider correlation with process monitoring and command line to detect anomalous processes execution and command line arguments associated to traffic patterns (e.g. monitor anomalies in use of files that do not normally initiate connections for respective protocol(s)). |
| Network Traffic Flow |
Monitor network data for uncommon data flows. Processes utilizing the network that do not normally have network communication or have never been seen before are suspicious. |